<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        html,body{
            background-color: #22334b;
        }
        .circle{
            background-color: yellow;
            width: 40px;
            height: 40px;
            margin: 15px;
            opacity: 0;
            border:2px solid red;
            transition: opacity .8s;
        }
        .circle:hover{
            opacity: 1;
        }
    </style>
</head>
<body>
    <div class="circle"></div>
    <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.js"></script>
    <script>
        var cc = function(){
            var $circle = $('<div class="circle"></div>')
            $('body').append($circle)
        }
    </script>
</body>
</html>